Question

Mendel crossed peas having round seeds and yellow cotyledons (seed leaves) with peas having wrinkled seeds and green cotyledons. All the \(F_{1}\) plants had round seeds with yellow cotyledons. Diagram this cross through the \(\mathrm{F}_{2}\) generation, using both the Punnett square and forked-line, or branch diagram, methods.

Short answer

In Mendel's pea experiment, given the traits for seed shape (round or wrinkled) and cotyledon color (yellow or green), we determined the F2 generation genotypes using both Punnett square and forked-line methods. The F2 generation genotypes are distributed as follows: 1 RRYY (round seeds, yellow cotyledons), 2 RrYY (round seeds, yellow cotyledons), 1 rrYY (wrinkled seeds, yellow cotyledons), 2 RRYy (round seeds, green cotyledons), 4 RrYy (round seeds, green cotyledons), 2 rrYy (wrinkled seeds, green cotyledons), 1 RRyy (round seeds, green cotyledons), 2 Rryy (round seeds, green cotyledons), and 1 rryy (wrinkled seeds, green cotyledons).

Step-by-step solution

Determine the F1 generation genotypes

Using the Punnett square method, we will find the possible genotype combinations for the F1 generation. Since both traits are inherited independently, we only need to cross the genotypes for each trait separately and then combine the results. Seed shape (R and r) cross: ``` R R r Rr Rr r Rr Rr ``` Cotyledon color (Y and y) cross: ``` Y Y y Yy Yy y Yy Yy ``` Combine the two results: all F1 generation plants have the genotype RrYy (round seeds, yellow cotyledons).

Set up the F2 generation genotypes

For the F2 generation, we will need to cross the F1 generation plants (RrYy) with themselves. Again, we will first cross the genotypes for seed shape and cotyledon color separately and then combine the results.

Determine the F2 generation seed shape genotypes using the Punnett square method

Cross the Rr genotype for seed shape (for F1 plants) with itself: ``` R r R RR Rr r Rr rr ``` We have the genotypes: RR (1), Rr (2), and rr (1) for the F2 generation seed shape.

Determine the F2 generation cotyledon color genotypes using the Punnett square method

Cross the Yy genotype for cotyledon color (for F1 plants) with itself: ``` Y y Y YY Yy y Yy yy ``` We have the genotypes: YY (1), Yy (2), and yy (1) for the F2 generation cotyledon color.

Combine the F2 generation results using the forked-line method

Now we can combine the results from steps 3 and 4 using the forked-line method. * Seed shape: 1 (RR) : 2 (Rr) : 1 (rr) * Cotyledon color: 1 (YY) : 2 (Yy) : 1 (yy) Using forked-line method: ``` 1 (RRYY) : 2 (RrYY) : 1 (rrYY) // seed shape combined with YY 2 (RRYy) : 4 (RrYy) : 2 (rrYy) // seed shape combined with Yy 1 (RRyy) : 2 (Rryy) : 1 (rryy) // seed shape combined with yy ``` The F2 generation genotypes are distributed as follows: 1 RRYY, 2 RrYY, 1 rrYY, 2 RRYy, 4 RrYy, 2 rrYy, 1 RRyy, 2 Rryy, and 1 rryy.